单项选择题

有以下程序:
#include <iostream>
using namespace std;
class sample
private:
int n;
public:
sample()
sample(int m)
n=m;
void addvalue(int m)
sample s;
s.n=n+m;
*this=s;
void disp ()
cout<<"n="<<n<<endl;
;
int main()
sample s(10);
s.addvalue(5);
s.disp();
return 0;
程序运行后的输出结果是

A.n=10
B.n=5
C.n=15
D.n=20